Method and Apparatus Providing Increased UVLED Intensity and Uniform Curing of Optical-Fiber Coatings

ABSTRACT

A UVLED apparatus and a related method provide increased UVLED intensity to promote efficient curing of a coated glass fiber. The apparatus employs a plurality of UVLED sources, each UVLED source emitting an oscillating output of ultraviolet radiation. Typically, at least two of the UVLED sources have oscillating outputs of ultraviolet radiation that are out of phase with one another. During curing, an incompletely cured coating on a glass fiber absorbs electromagnetic radiation emitted from the UVLED sources.

CROSS-REFERENCE TO PRIORITY APPLICATION

This application claims the benefit of U.S. Patent Application No.61/372,312 for a Method and Apparatus Providing Increased UVLEDIntensity (filed Aug. 10, 2010), which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present invention embraces an apparatus and a method for curingcoatings on drawn glass fibers.

BACKGROUND

Glass fibers are often protected from external forces with one or morecoating layers. Typically, two or more layers of coatings are appliedduring the optical-fiber drawing process (i.e., whereby a glass fiber isdrawn from an optical preform in a drawing tower). A softer innercoating layer typically helps to protect the glass fiber frommicrobending. A harder outer coating layer typically is used to provideadditional protection and to facilitate handling of the glass fiber. Thecoating layers may be cured, for example, using heat or ultraviolet (UV)light.

UV curing requires that the coated glass fiber be exposed to highintensity UV radiation. Curing time can be reduced by exposing thecoating to higher intensity UV radiation. Reducing curing time isparticularly desirable to permit an increase in fiber drawing linespeeds and thus optical-fiber production rates.

Mercury lamps (e.g., high-pressure mercury lamps or mercury xenon lamps)are commonly used to generate the UV radiation needed for UV curing. Onedownside of using mercury lamps is that mercury lamps require asignificant amount of power to generate sufficiently intense UVradiation. For example, UV lamps used to cure a single coated fiber(i.e., one polymeric coating) may require a collective power consumptionof 50 kilowatts.

Another shortcoming of mercury lamps is that much of the energy used forpowering mercury lamps is emitted not as UV radiation but rather asheat. Accordingly, mercury lamps must be cooled (e.g., using a heatexchanger) to prevent overheating. In addition, the undesirable heatgenerated by the mercury lamps may slow the rate at which theoptical-fiber coatings cure.

Furthermore, mercury lamps generate a wide spectrum of electromagneticradiation, such as electromagnetic radiation having wavelengths of lessthan 200 nanometers and greater than 700 nanometers (i.e., infraredlight). Typically, UV radiation having wavelengths of between about 300nanometers and 400 nanometers is useful for curing UV coatings. Thus,much of the electromagnetic radiation generated by mercury bulbs iswasted (e.g., 90 percent or more). Additionally, glass fibers typicallypossess a diameter of about 125 microns or less, which, of course, ismuch smaller than the mercury bulbs. Consequently, most of the UVradiation emitted by the mercury lamps does not reach the glass fiber'suncured coating (i.e., the energy is wasted).

It may thus be advantageous to employ UVLEDs to cure glass-fibercoatings as an alternative to conventional mercury lamps. UVLEDstypically require significantly less energy and correspondingly generatemuch less heat energy than conventional UV lamps.

By way of example, U.S. Pat. No. 7,022,382 (Khudyakov et al.), which ishereby incorporated by reference in its entirety, discloses the use ofUV lasers (e.g., continuous or pulsed lasers) for curing optical-fibercoatings. U.S. Patent Application Publication No. 2003/0026919 (Kojimaet al.), which is hereby incorporated by reference in its entirety,discloses the use of ultraviolet light emitting diodes (UVLEDs) forcuring optical-fiber coatings.

Although efficiency is an important consideration in selecting a curingapparatus, it is also desirable to employ a curing apparatus that iscapable of curing optical fibers quickly. In particular, it is desirableto employ a curing apparatus that is capable of curing optical fibersthat are moving at commercial draw speeds.

Therefore, a need exists for a curing apparatus that is capable ofoperating at commercial draw speeds and, as compared with a conventionalcuring apparatus employing mercury lamps, operates with improvedefficiency.

SUMMARY

Accordingly, in one aspect, the present invention embraces a UVLEDapparatus for curing in situ optical-fiber coatings (i.e., on a glassfiber).

An exemplary apparatus for curing a coated glass fiber includes a cavitythat defines a curing axis. A first UVLED array is positioned within thecavity. The first UVLED array includes a plurality of UVLED sources,each of which has (or is otherwise configured to have) a variable (e.g.,oscillating) output x_(n)(t) of UV radiation having a maximum outputintensity x_(n)(t)_(max) and a minimum output intensity x_(n)(t)_(min).The maximum output intensity x_(n)(t)_(max) of each of the UVLED sourcesis greater than can be achieved by driving each UVLED source at itsrespective maximum rated current. Typically, at least two of the UVLEDsources have oscillating outputs of UV radiation that are out of phasewith one another. In one embodiment, the apparatus includes a controllerthat is capable of adjusting the intensity and/or phase of theoscillating outputs of the UVLED sources.

In another aspect, the present invention embraces a method of curing acoating on a glass fiber. A glass fiber having an incompletely curedcoating is passed at a line speed v_(f) through a cavity and along acuring axis that is defined by the cavity. A plurality of UVLEDs thatdefine a first UVLED array are driven at a current that is greater thanthe maximum rated current of the UVLED sources. Each UVLED source has anoscillating output x_(n)(t) of UV radiation having a maximum outputintensity x_(n)(t)_(max) and a minimum output intensity x_(n)(t)_(min).The maximum output intensity x_(n)(t)_(max) of each of the UVLED sourcesis typically greater than could be achieved if each UVLED source wasdriven at its maximum rated current. UV radiation from the first UVLEDarray is emitted (e.g., into the cavity) to promote the curing of theglass-fiber coating.

During the in situ curing of an optical-fiber coating, the first UVLEDarray typically defines a normalized sum x_(total)(t,v_(f)):

${{x_{total}\left( {t,v_{f}} \right)} = {{x_{1}(t)} + {\sum\limits_{n = 2}^{k}{x_{n}\left( {t + \frac{d_{n}}{v_{f}}} \right)}}}},$

-   -   k=number of UVLED sources in the first UVLED array,    -   d_(n)=distance along the curing axis from a first UVLED source        to an n^(th) UVLED source.        To ensure even curing of the optical-fiber coating,        x_(total)(t,v_(f)) typically has a substantially constant value        at a given line speed.

The foregoing illustrative summary, as well as other exemplaryobjectives and/or advantages of the invention, and the manner in whichthe same are accomplished, are further explained within the followingdetailed description and its accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts an exemplary apparatus for curing a coatedglass fiber according to one aspect of the present invention.

FIGS. 2 a-2 d schematically depict exemplary UVLED source outputwaveforms.

FIG. 3 schematically depicts a perspective view of an exemplaryapparatus for curing a coated glass fiber according to another aspect ofthe present invention.

FIG. 4 schematically depicts a cross-sectional view of an exemplaryapparatus for curing a coated glass fiber according to an aspect of thepresent invention.

FIG. 5 schematically depicts the relationship between UVLED emissionangle and UVLED efficiency for UVLEDs of various widths.

FIG. 6 schematically depicts a cross-sectional view of an exemplaryapparatus for curing a coated glass fiber according to yet anotheraspect of the present invention.

DETAILED DESCRIPTION

In one aspect, the present invention embraces an apparatus for curingglass-fiber coatings (e.g., primary coatings, secondary coatings, and/ortertiary ink layers). The apparatus typically employs one or more UVLEDarrays. As herein discussed, each UVLED array has a plurality of UVLEDsources that are capable of being driven beyond their normal operatingcurrent (e.g., overdriven beyond a UVLED source's maximum ratedcurrent).

In a particular embodiment depicted in FIG. 1, the apparatus 10 forcuring glass-fiber coatings includes a UVLED array 11 a (denoted by adotted circle) positioned within a cavity 12 (e.g., a substantiallycylindrical cavity). The interior of the cavity 12 defines a curingspace. In turn, the curing space defines a curing axis 13 along which adrawn glass fiber passes during the curing process.

The UVLED array 11 a includes a plurality of UVLED sources 14 a. Amounting plate 15 may be employed to provide structural support for theUVLED sources 14 a. FIG. 1 depicts the UVLED array 11 a having two UVLEDsources 14 a. Typically, each UVLED source is formed from a single lightemitting diode. That said, it is within the scope of the presentinvention to employ a plurality of small light emitting diodes to formeach UVLED source.

Typically, each UVLED source (e.g., a single UVLED or a plurality ofdiscrete UVLEDs) is overdriven to achieve a higher-than-normal outputintensity. In other words, each UVLED source is typically driven at ahigher-than-rated power and current (e.g., higher than its normaloperating current) so that each UVLED source has a maximum outputintensity that is greater than could be achieved using a UVLED source'smaximum rated current. For example, a UVLED source may be driven at acurrent 2-4 times its maximum rated current (e.g., three times itsmaximum rated current). For some UVLED sources, a three-fold increase incurrent results in up to an eight-fold increase in UV-radiation outputintensity.

Those having ordinary skill in the art will appreciate that a device'smaximum rated current is the maximum current that the device cancontinuously carry, while remaining within its temperature rating.Although each UVLED source is typically driven at a higher-than-ratedcurrent, each UVLED source is typically driven at its normal operatingvoltage.

The cure rate of an optical-fiber coating depends not only on the totalUV radiation dosage but also on the intensity of the UV radiation towhich the coating is exposed. As will be appreciated by those havingordinary skill in the art, it has been observed that an increase in theintensity of UV radiation results in a nonlinear (e.g., squared)increase in the cure rate of a coating. By overdriving UVLED sources,the cure rate of optical-fiber coatings can be increased, therebyenabling higher line speeds.

Relative to other UV radiation sources (e.g., mercury lamps), UVLEDsources typically generate a smaller amount of heat energy. That said,each UVLED source may produce increased heat as a result of beingoverdriven. High temperatures may cause problems for the UVLED sources,therefore, dissipating heat generated by each UVLED source is importantfor a number of reasons. First, excessive heat may slow the rate atwhich optical-fiber coatings cure. Furthermore, excessive heat can causethe temperature of the UVLED source to rise, which can reduceUV-radiation output. Indeed, continuous high-temperature exposure candramatically reduce the lifetime of a UVLED source (e.g., by permanentlydamaging the UVLED source).

To dissipate the heat energy created by each UVLED source 14 a, a heatsink 16 may be located behind each UVLED source 14 a (e.g., opposite theportion of the UVLED source 14 a that emits UV radiation). The heat sink16 may be one-inch square, for example, although other heat sink shapesand sizes are within the scope of the present invention.

The heat sink may be formed of a material suitable for conducting heat(e.g., brass, aluminum, or copper). Exemplary heat sinks may includefins or other protrusions that facilitate air cooling of the heat sink.

The heat sink may include a heat exchanger that employs a liquid coolant(e.g., chilled water), which circulates within the heat exchanger todraw heat from the UVLED. Alternatively, a piezoelectric heat exchangermay be mounted on the heat sink.

To further reduce UVLED-source overheating, each UVLED source typicallyhas an oscillating (e.g., pulsed) output. In other words, each UVLEDsource typically has a repetitively variable output. For example, aUVLED source may be pulsed between high-power (e.g., on) and low-power(e.g., off) states. Although each UVLED source is typically off in itslow-power state, each UVLED source may alternatively remain on in itslow-power state, albeit having reduced output intensity. The low-power(e.g., off) state provides time for the UVLED source to cool and recoverbefore the next high-power state.

In one embodiment, pulsed UVLED sources may generate a waveform thatapproximates a square wave (i.e., a rectangular pulse train having aduty cycle of 50 percent). Because a square wave has a duty cycle of 50percent, a UVLED source that generates an output approximating a squarewave will have high-power and low-power states of equal duration. Thatsaid, other duty cycles are within the scope of the present invention.For example, waveforms emitted by exemplary UVLED sources may have aduty cycle of greater than or less than 50 percent (e.g., a rectangularwaveform having a duty cycle of 25 percent, 33 percent, or 75 percent).

Although the UVLED sources typically generate an approximatelyrectangular waveform, other waveforms are within the scope of thepresent invention. For example, a UVLED source may generate anapproximately triangular, sawtooth, or sinusoidal waveform. Exemplary,square, triangular, sawtooth, and sinusoidal waveforms are depicted inFIGS. 2 a-2 d, respectively.

It is desirable to ensure that a coated glass fiber is evenly curedalong its length. As noted, the degree to which a coated glass fiber iscured is a function of both UV intensity and UV dosage. To ensure that acoated glass fiber is evenly cured along its length, it is typicallydesirable to expose the coated glass fiber to UV radiation of consistentintensity and dosage as it passes through a UVLED array.

That said, each UVLED source typically emits UV radiation of varyingintensity (e.g., oscillating between high-power and low-power states).Moreover, if the UVLED sources are located at different positions alongthe curing axis, it will take some time for a point on the coated glassfiber to move from one UVLED source to subsequent UVLED sources.Therefore, to ensure even curing of a coated glass fiber passing througha UVLED array, the high-power and low-power states of the UVLED sourcesshould be timed so that every point on the coated glass fiber passes thesame number of UVLED sources that are in a high-power state. In otherwords, the UVLED sources typically are timed to account for (i) theperiod and duty of the oscillating UVLED outputs and (ii) the time ittakes for a point on the coated glass fiber to move from one UVLEDsource to subsequent UVLED sources.

Accordingly, the waveforms (e.g., x_(n)(t)) generated by at least someof the UVLED sources usually are out of phase with one another (i.e.,have a phase difference). For example, one UVLED source within the UVLEDarray may be in a high-power state, while other UVLED sources are in alow-power state.

The foregoing notwithstanding, other than possibly having a phasedifference, the UVLED sources within an array typically havesubstantially identical waveforms. That said, it is within the scope ofthe present invention for the UVLED sources within an array to havevarying waveforms. For example, a UVLED array may employ two UVLEDsources, the first UVLED source having a duty cycle of ⅓, and the secondUVLED source having a duty cycle of ⅔.

The number of UVLED sources within a UVLED array may be represented bythe variable k. Each UVLED source has an output defining a waveformx_(n)(t) with a period T (e.g., between about one and two seconds).

The duty cycle D of the UVLED source within the UVLED array may berepresented by the fraction A/B (i.e., the ratio of the time that aUVLED source is in a high-power state versus the total period length).For example, a duty cycle of ⅓ (e.g., about 33 percent) means that aUVLED source will be in its high-power state one third (i.e., ⅓) of thetime and in its low power state two thirds (i.e., ⅔) of the time.

As a practical matter, if the fraction representing the duty cycle(i.e., A/B) is irreducible, then to ensure even curing, the number ofUVLED sources in the UVLED array is typically at least B. For example, aUVLED array may employ five UVLED sources, each having a duty cycle of20 percent. By way of further example, a UVLED array may employ threeUVLED sources, each having a duty cycle of ⅔.

The position of each UVLED source may be defined by the cylindricalcoordinate system (i.e., r, θ, z). Using the cylindrical coordinatesystem and as described herein, the curing axis (i.e., the axis alongwhich a coated glass fiber passes during the curing process) defines az-axis.

Furthermore, as herein described and as will be understood by those ofordinary skill in the art, the variable r represents the perpendiculardistance of a point to the z-axis (i.e., the distance to the curingaxis). For UVLED sources employed in exemplary configurations, thevariable r is usually constant. Stated otherwise, the UVLED sources maybe positioned approximately equidistant from the curing axis (i.e., thez axis).

The variable θ describes, within a plane that is perpendicular to thez-axis, the angle between a reference direction and the projection to apoint. In other words and by reference to a Cartesian coordinate system(i.e., defining an x-axis, a y-axis, and a z-axis), the variable θdescribes the angle between a reference axis (e.g., the x-axis) and theorthogonal projection of a point onto the x-y plane.

Finally, the z variable describes the position of a reference pointalong the z-axis. In this regard, the UVLED sources are separated by adistance d_(n), which is defined as the distance along the z axis (i.e.,Δz) from the first UVLED source in the array to the other UVLED sourcesin the array. In other words, d₂ is the Δz between the first UVLEDsource and a second UVLED source, and d₃ is the Δz between the firstUVLED source and a third UVLED source.

The coated glass fiber has a line speed v_(f) (e.g., between about 10meters per second and 30 meters per second). Because a glass fiber istypically coated shortly after it is drawn, the line speed of a coatedglass fiber is typically the same as the draw speed of the glass fiber.

Each UVLED array has a cumulative radiation output (i.e., the sum of theoutputs of the UVLED sources). The cumulative radiation output of aUVLED array may be normalized to account for the line speed of a coatedglass fiber and the distance between UVLED sources. In other words, thecumulative radiation output of a UVLED array may be normalized toaccount for the time for a point on the coated glass fiber to travelalong the z axis between the UVLED sources within an array.

Therefore, each UVLED array defines (or is otherwise configured todefine) a normalized sum x_(total)(t,v_(f)) that is calculated accordingto the following equation:

${x_{total}\left( {t,v_{f}} \right)} = {{x_{1}(t)} + {\sum\limits_{n = 2}^{k}{x_{n}\left( {t + \frac{d_{n}}{v_{f}}} \right)}}}$

If each UVLED source within an array is located at the same positionalong the curing axis (i.e., having the same value with respect to the zaxis), then:

${x_{total}\left( {t,v_{f}} \right)} = {\sum\limits_{n = 1}^{k}{x_{n}(t)}}$

In a typical embodiment, x_(total)(t,v_(f)) has a substantially constantvalue for a given line speed v_(f) (i.e., assuming a constant linespeed). In this regard, when x_(total)(t,v_(f)) has a substantiallyconstant value, a glass fiber passing through the UVLED array is exposedto UV radiation of consistent intensity and dosage. Therefore, it isdesirable to coordinate the outputs of the UVLED sources (e.g., bycarefully selecting the phase, period, and/or duty cycle of theUVLED-source outputs) to ensure that x_(total)(t,v_(f)) has asubstantially constant value.

By way of example, a UVLED array may have B UVLED sources, eachgenerating a rectangular pulse train having a duty cycle D that is equalto A/B (i.e., representing the ratio of the time that a UVLED source isin a high-power state versus total period length). The rectangular pulsetrains generated by the UVLED sources have a maximum value (i.e.,maximum output intensity) x_(n)(t)_(max) and a minimum value (i.e.,minimum output intensity) x_(n)(t)_(min). If such an exemplary UVLEDarray defines a substantially constant x_(total)(t,v_(f)), and assumingthat each UVLED source in the array has substantially the same maximumoutput intensity x_(n)(t)_(max), thenx_(total)(t,v_(f))≈A(x_(n)(t)_(max)+x_(n)(t)_(min)). In other words, ifx_(total)(t,v_(f)) is substantially constant, then any point on thecoated glass fiber will pass A UVLED sources that are in a high-powerstate.

By way of further example, a UVLED array may employ two pulsed UVLEDsources. The distance from the first UVLED source to the second UVLEDsource (i.e., d₂) is 100 millimeters. The coated glass fiber that isbeing cured has a line speed v_(f) of 10 meters per second.

Each UVLED source generates a square wave output having a duty cycle of50 percent and a period of one second. The first UVLED source generatesa waveform x₁(t) that is equal to:

${x_{1}(t)} = {{\frac{1}{2}{{sgn}\left( {\sin \left( {2\pi \; t} \right)} \right)}} + \frac{1}{2}}$

The second UVLED source generates a waveform x₂(t) that is equal to:

${x_{2}(t)} = {{\frac{1}{2}{{sgn}\left( {\sin \left( {{2\pi \; t} - {\frac{51}{50}\pi}} \right)} \right)}} + \frac{1}{2}}$

Accordingly, x_(n)(t)_(max) is equal to 1 (i.e., represented here as aunitless 1) and x_(n)(t)_(min) is equal to 0. The normalized sumx_(total)(t,v_(f)) is equal to x₁(t)+x₂(t+d_(n)/v_(f)), thereforex_(total)(t,v_(f)) is equal to 1 (i.e., represented here as a unitless1). Because x_(total)(t,v_(f)) is equal to a constant value, the coatedglass fiber is exposed to UV radiation of consistent intensity anddosage as it passes through the UVLED array.

The apparatus for curing glass-fiber coatings may include a plurality ofUVLED arrays. For example, FIG. 1 depicts the apparatus 10 having asecond UVLED array 11 b (denoted by a dotted circle). Although FIG. 1depicts each UVLED array 11 a and 11 b having two UVLED sources 14 a and14 b, the number of UVLED sources in each array may vary. Furthermore,the outputs of the UVLED sources in the first UVLED array may differfrom the outputs of the UVLED sources in the second UVLED array. Forexample, a first UVLED array may employ two UVLED sources, eachgenerating a rectangular pulse train with a duty cycle of 50 percent. Asecond UVLED array may employ four UVLED sources, each generating arectangular pulse train with a duty cycle of 25 percent. The UVLEDsources in the second array may generate a higher or lower intensityoutput than the UVLED sources in the first array.

Varying the UV intensity of different UVLED arrays may enhance thecuring of the glass-fiber coating. Depending on the curing properties ofa particular coating, it may be desirable to initially expose a coatedglass fiber to high intensity UV radiation. Alternatively, it may bedesirable to initially expose the optical fiber to lower intensity UVradiation (e.g., between about 10 percent and 50 percent of the maximumexposure intensity) before exposing the optical fiber to high intensityUV radiation (e.g., the maximum intensity to which the optical fiber isexposed). In this regard, initially exposing the optical fiber to lowerintensity UV radiation may be useful in controlling the generation offree radicals in an uncured coating. Those of ordinary skill in the artwill appreciate that if too many free radicals are present, many of thefree radicals may recombine rather than encourage the polymerization ofthe glass-fiber coating—an undesirable effect.

Furthermore, an apparatus as described herein may include a dark spacebetween one or more UVLED arrays. In other words, the apparatus mayinclude a space in which substantially no UV radiation is incident tothe coated glass fiber being cured. A pause in the curing processprovided by a dark space can help to ensure even and efficient curing ofthe optical-fiber coatings. In particular, a dark space may be useful inpreventing too many free radicals from being present in a glass-fibercoating before it is cured (i.e., dark space helps to controlfree-radical generation).

For example, it may be desirable to initially expose a coated glassfiber to low-power UV radiation from a first UVLED array. After passingthe coated glass fiber through the first UVLED array, the coated glassfiber may be passed through a dark space. After the coated glass fiberpasses through the dark space, it may be exposed to higher-power UVradiation from a second UVLED array to complete the curing process. Acuring apparatus employing dark space is disclosed in commonly assignedU.S. Pat. No. 7,322,122 for a Method and Apparatus for Curing a FiberHaving at Least Two Fiber Coating Curing Stages, which is herebyincorporated by reference in its entirety.

As depicted in FIG. 1, the apparatus 10 may include a controller 18 thatis electrically connected to the UVLED sources 14 a and 14 b. Thecontroller 18 may be capable of adjusting the UV radiation output fromthe UVLED sources 14 a and 14 b. In particular, the controller 18 maychange the period, duty cycle, intensity, and/or phase of the outputs ofthe UVLED sources 14 a and 14 b (e.g., in response to a change in linespeed).

In this regard, the line speed of a coated glass fiber may vary duringthe curing process. The line speed may be affected by changes to thedraw speed of the glass fiber; the draw speed of the glass fiber istypically adjusted during the drawing process to ensure a near-constantfiber thickness. Because the degree to which a coated glass fiber curesis a function of UV intensity and dosage, a change in line speed canundesirably affect the degree to which a coated glass fiber cures (e.g.,by undesirably undercuring or overcuring portions of the coated glassfiber).

To prevent undercuring and/or overcuring, the output intensity of eachUVLED source may be increased at higher line speeds and decreased atlower line speeds, resulting in a change in the maximum output intensityx_(n)(t)_(max) of the UVLED sources. Furthermore, the phase of theUVLED-source outputs may be adjusted to ensure that the normalizedx_(total)(t,v_(f)) for each UVLED array defines a substantially constantvalue for a given line speed. At different line speeds,x_(total)(t,v_(f)) may define different substantially constant values.

The line speed of a coated glass fiber may be measured using a sensorthat is connected to the controller. The sensor then transmits the linespeed data to the controller, which can adjust the output of the UVLEDsources. For example, the output intensity of the UVLED sources may becontrolled by reducing (or increasing) the current flowing to theUVLEDs.

In a particular embodiment, the apparatus for curing glass-fibercoatings includes a UVLED array having a plurality of UVLED sourcespositioned within a cylindrical cavity (or a substantially cylindricalcavity) that has a reflective inner surface. To achieve the reflectiveinner surface, the cylindrical cavity may be made from stainless steel,polished aluminum, or metalized glass, such as silvered quartz, or othersuitable material. In addition, the interior of the cylindrical cavitydefines a curing space. In turn, the curing space defines a curing axisalong which a drawn glass fiber passes during the curing process.

Typically, a protective tube surrounds the curing axis. By way ofexample, a transparent quartz tube (e.g., a quartz tube that issubstantially transparent to UV radiation emitted by the UVLED sources)having a diameter of about 24 millimeters and a thickness of about 2millimeters may be employed as a protective tube. In another embodiment,the protective tube (e.g., a transparent quartz tube) may have adiameter of about 10 millimeters and a thickness of about 1 millimeter.In general, it is thought that employing a smaller protective tube wouldimprove curing efficiency (i.e., reduce UV radiation waste).

The protective tube prevents curing byproducts from damaging and/orfouling the UVLED sources within the cylindrical cavity. In this regard,volatile components of the optical-fiber coating have a tendency toevaporate during curing. In the absence of a protective tube, thesecuring byproducts can precipitate onto both the UVLEDs and the cavity'sreflective inner surface. The protective tube can also prevent uncuredcoating (e.g., delivered by a coating applicator) from beinginadvertently deposited within the cylindrical cavity (e.g., spilledonto the UVLED sources and/or the cavity's reflective inner surface).

An inert gas (e.g., nitrogen) or gas mixture (e.g., nitrogen and oxygen)may be introduced into the protective tube to provide an oxygen-free ora reduced-oxygen environment around an optical fiber as its coating isbeing cured. In this regard, it has been observed that having a smallamount of oxygen may promote efficient curing. Accordingly, theprotective tube may provide an environment having between about 0.1percent and 5 percent oxygen, such as between about 0.2 percent and 3percent oxygen (e.g., about 0.31 percent oxygen). Providing areduced-oxygen environment around the coated glass fiber seems to helpreduce the consumption of free radicals by the oxygen.

Furthermore, the gas (e.g., nitrogen and/or oxygen) flowing through theprotective tube may be heated, such as by employing one or more heatrings positioned around (i) the protective tube and/or (ii) a pipesupplying the gas. Alternatively, the gas flowing through the protectivetube may be heated using infrared heaters. Heating the gas flow helps toremove unreacted coating components (e.g., coating monomers) and/orunwanted byproducts present in the cured coating.

In a typical embodiment, the cylindrical cavity has a non-circularelliptical cross-section. In other words, the cylindrical cavity usuallyhas the shape of an elliptic cylinder. By way of illustration, anexemplary elliptic cylinder has a major axis length of 54 millimetersand a minor axis length of 45.8 millimeters. For an elliptic cylinder,the curing axis corresponds with one of the two line foci defined by theelliptic cylinder. Moreover, it is thought that the cylinder'selliptical shape can be modified to compensate for the deleteriouseffects that may be caused by the protective tube (e.g., refraction andreflection).

It will be appreciated by those having ordinary skill in the art that aUVLED does not emit UV radiation only toward a point or line, but ratheremits UV radiation in many directions. Thus, most of the UV radiationemitted by a UVLED source will not directly strike a glass-fiber coatingto effect curing. In curing an optical-fiber coating, however, it isdesirable that as much UV radiation as possible strike the optical fiber(i.e., a coated glass fiber). As will be understood by those havingordinary skill in the art, curing occurs when UV radiation is absorbedby photoinitiators in the glass-fiber coating.

Accordingly, the reflective surface of the cylindrical cavity canreflect otherwise misdirected UV radiation onto an optical fiber forcuring, thus reducing wasted energy. Moreover, for a cylindrical cavityhaving an elliptical cross-section, any electromagnetic radiation thatis emitted from one line focus (regardless of direction) will bedirected toward the other line focus after being reflected at the innersurface of the cylinder.

Accordingly, in one embodiment each UVLED source may be positioned alongthe other line focus (i.e., the line focus that does not correspond witha curing axis) such that each UVLED source emits UV radiation in thegeneral direction of the curing axis. In this regard, FIGS. 2 and 3depict an exemplary apparatus for curing a coated glass fiber. Theapparatus includes a cavity segment 20. The cavity segment 20 defines asubstantially cylindrical cavity 25 having an elliptical shape and areflective inner surface. The cavity 25 defines a first line focus 21and a second line focus 22. One or more UVLED sources 24 are positionedalong the first line focus 21.

In one embodiment, the cavity segment 20 may include a plurality ofUVLED sources 24 positioned contiguously to one another along the firstline focus 21 (i.e., directly stacked). In another embodiment, adjacentUVLED sources may be vertically separated by a space of at least about 5millimeters (e.g., at least about 10 millimeters). The second line focus22 further defines a curing axis along which a coated glass fiber 26passes so it can be cured. As depicted in FIG. 4, UV rays 23 emittedfrom the UVLED source 24 may reflect off the inner surface of the cavity25 such that the reflected UV rays 23 are incident to the coated glassfiber 26.

To facilitate uniform curing of the coated glass fiber 26, some of theUVLED sources 24 may be differently oriented. The cavity segment 20typically includes a single UVLED source positioned within a particularhorizontal plane. In an alternative embodiment, multiple UVLEDs may bepositioned (e.g., at a point other than the first focal line) within ahorizontal plane to promote more uniform curing of the glass fiber.

In another embodiment, an apparatus for curing a coated glass fiber mayinclude a plurality of differently oriented cavity segments. Each cavitymay have a common curing axis (e.g., the second focal line), but adifferent first line focus.

As depicted in FIG. 3, a second cavity segment 30 for curing a glassfiber may have a different orientation than the first cavity segment 20(e.g., the second cavity segment 30 may have UVLED sources positionedalong a line focus 31 that differs from the first line focus 21). Asfurther illustrated in FIG. 3, the second cavity segment 30 is rotated180 degrees relative to the orientation of the first cavity segment 20.That said, various degrees of rotation may separate adjacent cavitysegments. By way of non-limiting illustration, a 45-degree rotation, a90-degree rotation, or a 135-degree rotation may separate adjacentcavity segments while maintaining the common curing axis.

In this regard, the positioning of a plurality of cavity segments in athree-dimensional arrangement may be defined by the cylindricalcoordinate system (i.e., r, θ, z). Using the cylindrical coordinatesystem, the curing axis defines a z-axis. Furthermore, as hereindescribed and as will be understood by those having ordinary skill inthe art, the variable r is the perpendicular distance of a point to thez-axis. The variable θ describes the angle in a plane that isperpendicular to the z-axis. In other words and by reference to aCartesian coordinate system (i.e., defining an x-axis, a y-axis, and az-axis), the variable θ describes the angle between a reference axis(e.g., the x-axis) and the orthogonal projection of a point onto the x-yplane. Finally, the z variable describes the height or position of areference point along the z-axis.

By way of non-limiting example, a plurality of cavity segments havingthe same elliptical dimensions may be positioned in a helicalarrangement with the first cavity segment at the position (1, 0, 0),where r is fixed at a constant distance (i.e., represented here as aunitless 1). Additional cavity segments may be positioned, for example,every 90 degrees (i.e., n/2) with a Az of 1 (i.e., a positional stepchange represented here as a unitless 1). Thus, a second cavity segmentwould have the coordinates (1, π/2, 1), a third cavity segment wouldhave the coordinates (1, π, 2), and a fourth cavity segment would havethe coordinates (1, 3π/2, 3), thereby defining a helical configuration.In other words, the respective cavity segments are rotated around thecuring axis.

That said, the respective distances r and z need not be equivalent.Moreover, the several cavity segments in an arrangement as hereindisclosed need not be offset by 90 degrees (e.g., π/2, π, 3π/2, etc.).For example, the respective cavity segments may be offset by 60 degrees(e.g., π/3, 2π/3, π, etc.) or by 120 degrees (e.g., 2π/3, 4π/3, 2π,etc.). Indeed, the cavity segments in an arrangement as discussed hereinneed not follow a regularized helical rotation.

Applicant has discovered that the protective tube interferes with the UVradiation directed toward the curing axis.

By way of example, Applicant simulated directing a 0.1-millimeter wideUVLED having an emission pattern of cos^(1.5)(Φ) directly toward (i.e.,employing an emission angle of 0 degrees) a target having a diameter of250 microns, the approximate diameter of a representative optical fiber.As used herein, the size of a UVLED refers to its actual size or, if theUVLED is rescaled with a lens, its effective size. The simulationpositioned the point source and the target at opposite foci within areflective elliptic cylinder having a major axis length of 54millimeters and a minor axis length of 45.8 millimeters. In the absenceof a protective tube, nearly 100 percent of the UV rays hit the target.

When a protective tube having a diameter of 24 millimeters and arefractive index of 1.5 is employed, however, only about 75 percent ofthe UV rays hit the 250-micron target. In this regard, UV rays having anincidence angle other than approximately 90 degrees with the protectivetube can be undesirably refracted or reflected.

Applicant also simulated directing the UVLED toward a 250-micron targetsurrounded by a protective tube while employing an emission angle of 90degrees rather than 0 degrees. Table 1 (below) shows UVLED efficiency(i.e., the percent of UV radiation hitting a 250-micron target) atrespective emission angles of 0 degrees and 90 degrees for UVLEDs ofvarious widths.

TABLE 1 (UVLED Efficiency) UVLED UVLED Efficiency UVLED Efficiency Width(mm) (0° emission angle) (90° emission angle) 0.1 77 100 0.2 77 79 0.377 61 0.4 77 50 0.5 76 43 1 45 25 1.5 31 17 2 24 13 2.5 19 11

Table 2 (below) shows UVLED efficiency for a UVLED having a width (oreffective width) of 0.1 mm.

TABLE 2 (UVLED Efficiency) Elliptic Elliptic Cylinder Cylinder MajorMinor Protective Axis Axis Tube Emission UVLED Width Width DiameterEmission Angle Efficiency (mm) (mm) (mm) Pattern (degrees) (percentage)54 45.8 — cos² (Φ) 0 100 54 45.8 24 cos² (Φ) 0 75 54 45.8 24 cos^(1.5)(Φ) 0 77 54 45.8 24 cos^(1.5) (Φ) 90 100 60 51.8 24 cos^(1.5) (Φ) 0 7860 51.8 24 cos^(1.5) (Φ) 90 100

Applicant further simulated UVLED efficiency for various emission anglesusing various UVLEDs, where (i) the reflective elliptic cylinder had amajor axis length of 54 millimeters and a minor axis length of 45.8millimeters, (ii) the protective tube had a diameter of 24 millimeters,and (iii) the UVLED had an emission pattern of cos^(1.5)(Φ). For thisapparatus configuration, FIG. 5 graphically depicts the relationshipbetween UVLED emission angle and UVLED efficiency for UVLEDs of variouswidths. In brief, FIG. 5 shows that for a UVLED having a width of lessthan 0.5 millimeter, employing an emission angle of more than 0 degreesimproves UVLED efficiency.

For UVLEDs having a width (or effective width) of less than about 0.5millimeter (as deployed in the foregoing apparatus configuration),emission angle α can be optimally calculated in accordance with thefollowing equation: α=733.33x²−690x+161.67, where x is the width of theUVLED, x<0.5 millimeter, and the UVLED has an emission pattern ofcos^(1.5)(Φ). Moreover, for the foregoing apparatus configuration, theUVLED efficiency can be optimally calculated in accordance with thefollowing equation:

UVLED efficiency=1001.3x³+1166.1x²−461.6x+140.45, where x is the widthof the UVLED, x<0.5 millimeter, and the UVLED has an emission pattern ofcos^(1.5)(Φ).

More generally and in accordance with the present invention, the optimumemission angle is typically at least about 30 degrees, such as between30 degrees and 100 degrees (e.g., about 90 degrees for a UVLED having awidth of about 0.3 millimeter or less), more typically between about 30degrees and 60 degrees (e.g., about 45 degrees for a UVLED having awidth of about 0.22 millimeter), between each UVLED source and the majoraxis of the elliptical cylinder. In this regard, ever smaller UVLEDs mayfacilitate the deployment of a curing apparatus that can efficientlyemploy emission angles approaching 180 degrees. By way of example, sucha curing apparatus might employ emission angles greater than about 100degrees, such as between about 120 degrees and 150 degrees (e.g., about135 degrees). When a protective tube is present within the ellipticalcylinder (i.e., surrounding the curing axis), employing an angled UVLEDsource in this way will provide improved UV absorption during curing.

FIG. 6 depicts an exemplary apparatus 50 for curing a coated glass fiber26 in accordance with the present invention. In particular, theapparatus 50 employs one or more angled UVLED sources 24 positionedwithin a substantially cylindrical cavity 25 having an elliptical shapeand having a reflective inner surface. The cavity 25 defines a firstline focus 21 and a second line focus 22. The second line focus 22defines a curing axis. A coated glass fiber 26 passes along the curingaxis during curing. Finally, a protective tube 35 surrounds the curingaxis and the coated glass fiber 26.

The cavity 25 also defines a major axis 34 that intersects the firstline focus 21 and the second line focus 22. One or more UVLED sources 24are positioned along the first line focus 21. Each UVLED source 24 emitsUV rays 23 in a distinctive emission pattern. In general, an emissionpattern has a line of average emission L_(avg) 23 a (i.e., an average ofall the UV rays emitted by the UVLED source 24).

In an exemplary embodiment, an UVLED source 24 is angled away from thecoated glass fiber 26. In particular, the UVLED source 24 is positionedso that an emission angle α is defined between the line of averageemission L_(avg) 23 a and the elliptical cylinder's major axis 34. Theemission angle α is typically between about 30 degrees and 100 degrees(e.g., between 30 degrees and 60 degrees), more typically between about40 degrees and 50 degrees (e.g., 45 degrees).

Although the emission angle α is typically calculated relative to theline of average emission L_(avg) for a UVLED source (e.g., a singleUVLED), it is within the scope of the invention to describe the emissionangle α relative to a line defined by a UVLED source's median or mode(i.e., a line of maximum emission L_(max)).

Those having ordinary skill in that art will appreciate that the UVradiation emitted from a UVLED is not emitted from a single point.Therefore, and because of the small size of a coated glass fiber (e.g.,a 250-micron diameter), it is desirable to use small UVLED sources(e.g., a 3-millimeter square UVLED or a 1-millimeter square UVLED). Ingeneral, a greater percentage of reflected UV radiation will be incidentto the coated glass fiber using a small UVLED as compared to using alarger UVLED.

Moreover, each UVLED source may include a lens (e.g., a convex lens,such as a biconvex or plano-convex lens) for focusing emitted UVradiation. In particular, each lens may have a focus at one of the twoline foci (e.g., the line focus not defining a curing axis). Forexample, a cylindrical lens with a high numerical aperture can be usedto rescale a 3-millimeter square UVLED, so that it has an effectivewidth of about 0.4 millimeter or less at the line focus. By including alens with each UVLED, the efficiency of the apparatus may be furtherenhanced.

In an alternative embodiment, the apparatus for curing a coated glassfiber may employ one or more optical fibers (e.g., one or more multimodeoptical fibers) to transmit UV radiation. In this regard, these opticalfibers are typically positioned along the first line focus of theapparatus as an alternative to positioning UVLED sources along the firstline focus. Typically, each optical fiber is coupled to one or moresources of UV radiation, such as a UVLED source. By way of example, aplurality of small UVLEDS may be coupled to a plurality of opticalfibers in a one-to-one relationship (e.g., 20 UVLEDS and 20 opticalfibers). Thereupon, the optical fibers may be arranged in variousconfigurations at or near the first line focus.

Moreover, at least one—and typically each—optical fiber is oriented atthe first line focus to provide an emission angle of between about 30degrees and 120 degrees (e.g., between 45 degrees and 90 degrees). Suchoptical fibers typically employ a central glass fiber, but mayalternatively employ a central plastic fiber.

Moreover, the use of an optical fiber to transmit UV radiation into thecavity may facilitate the deployment of a curing apparatus that canefficiently employ emission angles approaching 180 degrees. By way ofexample, such a curing apparatus might employ emission angles between120 degrees and 180 degrees (e.g., about 150 degrees).

To simplify coupling with the UVLED source(s), multimode optical fibersare typically employed for purposes of UV-radiation transmission. Thatsaid, it is within the scope of the present invention to employsingle-mode optical fibers (e.g., holey glass fibers). An exemplarysingle-mode optical fiber is a large-mode-area fiber (LMA) that providesa Gaussian beam having a diameter of 0.1 millimeter or less. Anexemplary holey optical fiber is disclosed in commonly assigned U.S.patent application Ser. No. 12/692,161 for a Single-Mode Optical Fiber,filed Jan. 22, 2010, (Richard et al.), which is hereby incorporated byreference in its entirety.

To supplement the foregoing disclosure, this application incorporatesentirely herein by reference commonly assigned U.S. Patent ApplicationPublication No. US2010/0183821 A1 for a UVLED Apparatus for CuringGlass-Fiber Coatings, (Hartsuiker et al.); commonly assigned U.S. patentapplication Ser. No. 13/111,147 for a Curing Apparatus Employing AngledUVLEDs, filed May 19, 2011, (Molin); commonly assigned U.S. patentapplication Ser. No. 13/152,651 for a Curing Apparatus Having UV SourcesThat Emit Differing Ranges of UV Radiation, filed Jun. 3, 2011, (Gharbiet al.); commonly assigned U.S. Patent Application No. 61/346,806 for aCuring Apparatus Employing Angled UVLEDs, filed May 20, 2010, (Molin);commonly assigned U.S. Patent Application No. 61/351,151 for a CuringApparatus Employing Angled UVLEDs, filed Jun. 3, 2010, (Molin); andcommonly assigned U.S. Patent Application No. 61/351,205 for a CuringApparatus Having UV Sources That Emit Differing Ranges of UV Radiation,filed Jun. 3, 2010, (Gharbi et al.). This application furtherincorporates entirely herein by reference U.S. Pat. No. 4,683,525; U.S.Pat. No. 4,710,638; U.S. Pat. No. 7,022,382; U.S. Pat. No. 7,173,266;U.S. Pat. No. 7,399,982; U.S. Pat. No. 7,498,065; and U.S. PatentApplication Publication No. 2003/0026919.

UVLEDs are capable of emitting wavelengths within a much smallerspectrum than conventional UV lamps. This promotes the use of more ofthe emitted electromagnetic radiation for curing. That said, the UVLEDapparatus (and its related system and method) disclosed herein may bemodified to employ mercury lamps and/or fusion lamps as radiationsources (e.g., a supplemental source of UV radiation if insufficientcuring is achieved using only UVLEDs).

In this regard, a UVLED source for use in the present invention may beany suitable UVLED that emits electromagnetic radiation havingwavelengths of between about 200 nanometers and 600 nanometers. By wayof example, the UVLED may emit electromagnetic radiation havingwavelengths of between about 200 nanometers and 450 nanometers (e.g.,between about 250 nanometers and 400 nanometers). In a particularexemplary embodiment, the UVLED may emit electromagnetic radiationhaving wavelengths of between about 300 nanometers and 400 nanometers.In another particular exemplary embodiment, the UVLED may emitelectromagnetic radiation having wavelengths of between about 350nanometers and 425 nanometers.

As noted, a UVLED typically emits a narrow band of electromagneticradiation. For example, the UVLED may substantially emit electromagneticradiation having wavelengths that vary by no more than about 30nanometers, typically no more than about 20 nanometers (e.g., a UVLEDemitting a narrow band of UV radiation mostly between about 375nanometers and 395 nanometers). It has been observed that a UVLEDemitting a narrow band of UV radiation mostly between about 395nanometers and 415 nanometers is more efficient than other narrow bandsof UV radiation.

Moreover, it has been observed that in some cases UVLEDs emitting UVradiation slightly above the wavelength at which a glass-fiber coatinghas maximum absorption (e.g., an absorption peak of about 360nanometers) promote more efficient polymerization than do UVLEDsemitting UV radiation at the wavelength at which the glass-fiber coatinghas maximum absorption. Accordingly, the UVLED apparatus may employUVLED sources that have a mean output wavelength at least about 10nanometers greater than the glass-fiber coating's targeted absorptionpeak (e.g., at least about 10 to 15 nanometers greater than a targetedabsorption peak). That said, it is within the scope of the presentinvention to employ UVLEDs that have a mean output wavelength withinabout 10 nanometers (e.g., within about 5 nanometers) of a targetedabsorption peak.

In this regard, although an exemplary UVLED source emits substantiallyall of its electromagnetic radiation within a defined range (e.g.,between 350 nanometers and 450 nanometers, such as between 370nanometers and 400 nanometers), the UVLED source may emit small amountsof electromagnetic radiation outside the defined range. In this regard,80 percent or more (e.g., at least about 90 percent) of the output(i.e., emitted electromagnetic radiation) of an exemplary UVLED sourceis typically within a defined range (e.g., between about 375 nanometersand 425 nanometers).

As noted, UVLEDs can have various emission patterns (e.g., far fieldpattern). By way of example, a UVLED employed in accordance with thepresent invention may have a substantially Lambertian emission pattern.In other embodiments, a UVLED source (e.g., a UVLED) may have a Gaussianor multimodal emission pattern. Another exemplary UVLED may have anemission pattern of cos^(1.5)(Φ) or cos²(Φ).

UVLEDs are typically much smaller than conventional UV lamps (e.g.,mercury bulbs). By way of example, the UVLED may be a 0.25-inch squareUVLED. The UVLED may be affixed to a platform (e.g., a 1-inch square orlarger mounting plate). Of course, other UVLED shapes and sizes arewithin the scope of the present invention. By way of example, a3-millimeter square UVLED may be employed in the apparatus according tothe present invention.

Each UVLED may have a power output of as much as 32 watts (e.g., a UVLEDhaving a power input of about 160 watts and a power output of about 32watts). That said, UVLEDs having outputs greater than 32 watts (e.g., 64watts) may be employed as such technology becomes available. UsingUVLEDs with higher power output may be useful for increasing the rate atwhich optical-fiber coatings cure, thus promoting increased productionline speeds.

Each UVLED source may be positioned at a distance of between about 1millimeter and 100 millimeters (e.g., typically between about 5millimeters and 30 millimeters) from the optical fiber to be cured(e.g., from the curing axis). More typically, each UVLED source ispositioned at a distance of about 25 millimeters from the optical fiberto be cured.

It will be further appreciated by those of ordinary skill in the artthat UVLEDs may absorb incident electromagnetic radiation, which mightdiminish the quantity of reflected UV radiation available for absorptionby the glass-fiber coating. Moreover, incident UV radiation can damage aUVLED. Therefore, in an apparatus for curing glass-fiber coatings havinga plurality of UVLEDs, it may be desirable to position the UVLEDs in away that reduces UV radiation incident to the UVLEDs. Accordingly, avertical space of at least about 10 millimeters may separate adjacentUVLEDs. Moreover, the UVLEDs may employ a reflective surface (e.g., asurface coating) that promotes reflection of incident electromagneticradiation yet permits the transmission of emitted electromagneticradiation.

Finally, glass fiber is typically rotated or otherwise subjected toperturbations during drawing operations to reduce unwanted dispersioneffects. It is thought that this may further enhance the curing processas herein described.

The foregoing description embraces the curing of one or more coatinglayers on a glass fiber. The disclosed apparatus, system, and method maybe similarly employed to cure a buffer layer onto an optical fiber or aribbon matrix around a plurality of optical fibers.

In accordance with the foregoing, the resulting optical fiber includesone or more coating layers (e.g., a primary coating and a secondarycoating). At least one of the coating layers—typically the secondarycoating—may be colored and/or possess other markings to help identifyindividual fibers. Alternatively, a tertiary ink layer may surround theprimary and secondary coatings.

For example, the resulting optical fiber may have one or more coatings(e.g., the primary coating) that comprise a UV-curable, urethaneacrylate composition. In this regard, the primary coating may includebetween about 40 and 80 weight percent of polyether-urethane acrylateoligomer as well as photoinitiator, such as LUCIRIN® TPO, which iscommercially available from BASF. In addition, the primary coatingtypically includes one or more oligomers and one or more monomerdiluents (e.g., isobornyl acrylate), which may be included, forinstance, to reduce viscosity and thereby promote processing. Exemplarycompositions for the primary coating include UV-curable urethaneacrylate products provided by DSM Desotech (Elgin, Ill.) under varioustrade names, such as DeSolite® DP 1011, DeSolite® DP 1014, DeSolite® DP1014XS, and DeSolite® DP 1016. An exemplary coating system is availablefrom Draka Comteq under the trade name COLORLOCK® ^(XS).

Each coating layer is typically cured before a subsequent coating layeris applied. For example, a coated glass fiber may pass through a firstcuring apparatus after a primary coating is applied. Once the primarycoating has cured, a secondary coating may be applied and cured using asecond curing apparatus. Alternatively, both the primary and secondarycoatings may be applied, after which the primary and secondary coatingsare cured concurrently.

Those having ordinary skill in the art will recognize that an opticalfiber with a primary coating (and an optional secondary coating and/orink layer) typically has an outer diameter of between about 235 micronsand about 265 microns (μm). The component glass fiber itself (i.e., theglass core and surrounding cladding layers) typically has a diameter ofabout 125 microns, such that the total coating thickness is typicallybetween about 55 microns and 70 microns.

With respect to an exemplary optical fiber achieved according to thepresent curing method, the component glass fiber may have an outerdiameter of about 125 microns. With respect to the optical fiber'ssurrounding coating layers, the primary coating may have an outerdiameter of between about 175 microns and about 195 microns (i.e., aprimary coating thickness of between about 25 microns and 35 microns),and the secondary coating may have an outer diameter of between about235 microns and about 265 microns (i.e., a secondary coating thicknessof between about 20 microns and 45 microns). Optionally, the opticalfiber may include an outermost ink layer, which is typically between twoand ten microns thick.

In an alternative embodiment, the resulting optical fiber may possess areduced diameter (e.g., an outermost diameter between about 150 micronsand 230 microns). In this alternative optical-fiber configuration, thethickness of the primary coating and/or secondary coating is reduced,while the diameter of the component glass fiber is maintained at about125 microns. By way of example, in such embodiments, the primary coatinglayer may have an outer diameter of between about 135 microns and about175 microns (e.g., about 160 microns), and the secondary coating layermay have an outer diameter of between about 150 microns and about 230microns (e.g., more than about 165 microns, such as 190-210 microns orso). In other words, the total diameter of the optical fiber is reducedto less than about 230 microns (e.g., about 200 microns).

Exemplary coating formulations for use with the apparatus and methoddescribed herein are disclosed in the following commonly assignedapplications, each of which is incorporated by reference in itsentirety: U.S. Patent Application No. 61/112,595 for aMicrobend-Resistant Optical Fiber, filed Nov. 7, 2008, (Overton);International Patent Application Publication No. WO 2009/062131 A1 for aMicrobend-Resistant Optical Fiber, (Overton); U.S. Patent ApplicationPublication No. US2009/0175583 A1 for a Microbend-Resistant OpticalFiber, (Overton); and U.S. Patent Application Publication No.US2010/0119202 A1 for a Reduced-Diameter Optical Fiber (Overton).

To supplement the present disclosure, this application incorporatesentirely by reference the following commonly assigned patents, patentapplication publications, and patent applications: U.S. Pat. No.4,838,643 for a Single Mode Bend Insensitive Fiber for Use in FiberOptic Guidance Applications (Hodges et al.); U.S. Pat. No. 7,623,747 fora Single Mode Optical Fiber (de Montmorillon et al.); U.S. Pat. No.7,587,111 for a Single-Mode Optical Fiber (de Montmorillon et al.); U.S.Pat. No. 7,356,234 for a Chromatic Dispersion Compensating Fiber (deMontmorillon et al.); U.S. Pat. No. 7,483,613 for a Chromatic DispersionCompensating Fiber (Bigot-Astruc et al.); U.S. Pat. No. 7,526,177 for aFluorine-Doped Optical Fiber (Matthijsse et al.); U.S. Pat. No.7,555,186 for an Optical Fiber (Flammer et al.); U.S. Patent ApplicationPublication No. US2009/0252469 A1 for a Dispersion-Shifted Optical Fiber(Sillard et al.); U.S. Patent Application Publication No. US2011/0044595A1 for a Transmission Optical Fiber Having Large Effective Area (Sillardet al.); International Patent Application Publication No. WO 2009/062131A1 for a Microbend-Resistant Optical Fiber, (Overton); U.S. PatentApplication Publication No. US2009/0175583 A1 for a Microbend-ResistantOptical Fiber, (Overton); U.S. Patent Application Publication No.US2009/0279835 A1 for a Single-Mode Optical Fiber Having Reduced BendingLosses, filed May 6, 2009, (de Montmorillon et al.); U.S. Pat. No.7,889,960 for a Bend-Insensitive Single-Mode Optical Fiber, (deMontmorillon et al.); U.S. Patent Application Publication No.US2010/0021170 A1 for a Wavelength Multiplexed Optical System withMultimode Optical Fibers, filed Jun. 23, 2009, (Lumineau et al.); U.S.Patent Application Publication No. US2010/0028020 A1 for a MultimodeOptical Fibers, filed Jul. 7, 2009, (Gholami et al.); U.S. PatentApplication Publication No. US2010/0119202 A1 for a Reduced-DiameterOptical Fiber, filed Nov. 6, 2009, (Overton); U.S. Patent ApplicationPublication No. US2010/0142969 A1 for a Multimode Optical System, filedNov. 6, 2009, (Gholami et al.); U.S. Patent Application Publication No.US2010/0118388 A1 for an Amplifying Optical Fiber and Method ofManufacturing, filed Nov. 12, 2009, (Pastouret et al.); U.S. PatentApplication Publication No. US2010/0135627 A1 for an Amplifying OpticalFiber and Production Method, filed Dec. 2, 2009, (Pastouret et al.);U.S. Patent Application Publication No. US2010/0142033 for an IonizingRadiation-Resistant Optical Fiber Amplifier, filed Dec. 8, 2009,(Regnier et al.); U.S. Patent Application Publication No. US2010/0150505A1 for a Buffered Optical Fiber, filed Dec. 11, 2009, (Testu et al.);U.S. Patent Application Publication No. US2010/0171945 for a Method ofClassifying a Graded-Index Multimode Optical Fiber, filed Jan. 7, 2010,(Gholami et al.); U.S. Patent Application Publication No. US2010/0189397A1 for a Single-Mode Optical Fiber, filed Jan. 22, 2010, (Richard etal.); U.S. Patent Application Publication No. US2010/0189399 A1 for aSingle-Mode Optical Fiber Having an Enlarged Effective Area, filed Jan.27, 2010, (Sillard et al.); U.S. Patent Application Publication No.US2010/0189400 A1 for a Single-Mode Optical Fiber, filed Jan. 27, 2010,(Sillard et al.); U.S. Patent Application Publication No. US2010/0214649A1 for an Optical Fiber Amplifier Having Nanostructures, filed Feb. 19,2010, (Burow et al.); U.S. Patent Application Publication No.US2010/0254653 A1 for a Multimode Fiber, filed Apr. 22, 2010, (Molin etal.); U.S. Patent Application Publication No. US2010/0310218 A1 for aLarge Bandwidth Multimode Optical Fiber Having a Reduced CladdingEffect, filed Jun. 4, 2010, (Molin et al.); U.S. Patent ApplicationPublication No. US2011/0058781 A1 for a Multimode Optical Fiber HavingImproved Bending Losses, filed Sep. 9, 2010, (Molin et al.); U.S. PatentApplication Publication No. US2011/0064367 A1 for a Multimode OpticalFiber, filed Sep. 17, 2010, (Molin et al.); U.S. Patent ApplicationPublication No. US2011/0069724 A1 for an Optical Fiber for Sum-FrequencyGeneration, filed Sep. 22, 2010, (Richard et al.); U.S. PatentPublication No. US2011/0116160 A1 for a Rare-Earth-Doped Optical FiberHaving Small Numerical Aperture, filed Nov. 11, 2010, (Boivin et al.);U.S. Patent Publication No. US2011/0123161 A1 for a High-Bandwidth,Multimode Optical Fiber with Reduced Cladding Effect, filed Nov. 24,2010, (Molin et al.); U.S. Patent Publication No. US2011/0123162 A1 fora High-Bandwidth, Dual-Trench-Assisted Multimode Optical Fiber, filedNov. 24, 2010, (Molin et al.); U.S. Patent Publication No.US2011/0135262 A1 for a Multimode Optical Fiber with Low Bending Lossesand Reduced Cladding Effect, filed Dec. 3, 2010, (Molin et al.); U.S.Patent Publication No. US2011/0135263 A1 for a High-Bandwidth MultimodeOptical Fiber Having Reduced Bending Losses, filed Dec. 3, 2010, (Molinet al.); U.S. Patent Publication No. US2011/0188826 A1 for a Non-ZeroDispersion Shifted Optical Fiber Having a Large Effective Area, filedJan. 31, 2011, (Sillard et al.); U.S. Patent Publication No.US2011/0188823 A1 for a Non-Zero Dispersion Shifted Optical Fiber Havinga Short Cutoff Wavelength, filed Jan. 31, 2011, (Sillard et al.); U.S.patent application Ser. No. 13/037,943 for a Broad-Bandwidth MultimodeOptical Fiber Having Reduced Bending Losses, filed Mar. 1, 2011,(Bigot-Astruc et al.); U.S. patent application Ser. No. 13/048,028 for aSingle-Mode Optical Fiber, filed Mar. 15, 2011, (de Montmorillon etal.); and U.S. patent application Ser. No. 13/175,181 for a Single-ModeOptical Fiber, filed Jul. 1, 2011, (Bigot-Astruc et al.).

To supplement the present disclosure, this application furtherincorporates entirely by reference the following commonly assignedpatents, patent application publications, and patent applications: U.S.Pat. No. 5,574,816 for Polypropylene-Polyethylene Copolymer Buffer Tubesfor Optical Fiber Cables and Method for Making the Same; U.S. Pat. No.5,717,805 for Stress Concentrations in an Optical Fiber Ribbon toFacilitate Separation of Ribbon Matrix Material; U.S. Pat. No. 5,761,362for Polypropylene-Polyethylene Copolymer Buffer Tubes for Optical FiberCables and Method for Making the Same; U.S. Pat. No. 5,911,023 forPolyolefin Materials Suitable for Optical Fiber Cable Components; U.S.Pat. No. 5,982,968 for Stress Concentrations in an Optical Fiber Ribbonto Facilitate Separation of Ribbon Matrix Material; U.S. Pat. No.6,035,087 for an Optical Unit for Fiber Optic Cables; U.S. Pat. No.6,066,397 for Polypropylene Filler Rods for Optical Fiber CommunicationsCables; U.S. Pat. No. 6,175,677 for an Optical Fiber Multi-Ribbon andMethod for Making the Same; U.S. Pat. No. 6,085,009 for Water BlockingGels Compatible with Polyolefin Optical Fiber Cable Buffer Tubes andCables Made Therewith; U.S. Pat. No. 6,215,931 for FlexibleThermoplastic Polyolefin Elastomers for Buffering Transmission Elementsin a Telecommunications Cable; U.S. Pat. No. 6,134,363 for a Method forAccessing Optical Fibers in the Midspan Region of an Optical FiberCable; U.S. Pat. No. 6,381,390 for a Color-Coded Optical Fiber Ribbonand Die for Making the Same; U.S. Pat. No. 6,181,857 for a Method forAccessing Optical Fibers Contained in a Sheath; U.S. Pat. No. 6,314,224for a Thick-Walled Cable Jacket with Non-Circular Cavity Cross Section;U.S. Pat. No. 6,334,016 for an Optical Fiber Ribbon Matrix MaterialHaving Optimal Handling Characteristics; U.S. Pat. No. 6,321,012 for anOptical Fiber Having Water Swellable Material for Identifying Groupingof Fiber Groups; U.S. Pat. No. 6,321,014 for a Method for ManufacturingOptical Fiber Ribbon; U.S. Pat. No. 6,210,802 for Polypropylene FillerRods for Optical Fiber Communications Cables; U.S. Pat. No. 6,493,491for an Optical Drop Cable for Aerial Installation; U.S. Pat. No.7,346,244 for a Coated Central Strength Member for Fiber Optic Cableswith Reduced Shrinkage; U.S. Pat. No. 6,658,184 for a Protective Skinfor Optical Fibers; U.S. Pat. No. 6,603,908 for a Buffer Tube thatResults in Easy Access to and Low Attenuation of Fibers Disposed WithinBuffer Tube; U.S. Pat. No. 7,045,010 for an Applicator for High-SpeedGel Buffering of Flextube Optical Fiber Bundles; U.S. Pat. No. 6,749,446for an Optical Fiber Cable with Cushion Members Protecting Optical FiberRibbon Stack; U.S. Pat. No. 6,922,515 for a Method and Apparatus toReduce Variation of Excess Fiber Length in Buffer Tubes of Fiber OpticCables; U.S. Pat. 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In the specification and/or figures, typical embodiments of theinvention have been disclosed. The present invention is not limited tosuch exemplary embodiments. The use of the term “and/or” includes anyand all combinations of one or more of the associated listed items. Thefigures are schematic representations and so are not necessarily drawnto scale. Unless otherwise noted, specific terms have been used in ageneric and descriptive sense and not for purposes of limitation.

1. A method of curing a coating on a glass fiber, comprising: passing aglass fiber having an incompletely cured coating at a line speed v_(f)through a cavity and along a curing axis that is defined by the cavity;emitting UV radiation from a first UVLED array into the cavity topromote the curing of the coating, the first UVLED array comprising aplurality of UVLED sources each of which emit an oscillating outputx_(n)(t) of UV radiation having a maximum output intensityx_(n)(t)_(max) and a minimum output intensity x_(n)(t)_(min); whereinthe first UVLED array defines a normalized sum x_(total)(t,v_(f)):${{x_{total}\left( {t,v_{f}} \right)} = {{x_{1}(t)} + {\sum\limits_{n = 2}^{k}{x_{n}\left( {t + \frac{d_{n}}{v_{f}}} \right)}}}},$k=number of the UVLED sources in the first UVLED array, d_(n)=distancealong the curing axis from a first UVLED source to an n^(th) UVLEDsource; wherein the first UVLED source and at least one other UVLEDsource in the first UVLED array are separated along the curing axis; andwherein, at a given line speed, x_(total)(t,v_(f)) has a substantiallyconstant value.
 2. The method according to claim 1, wherein each of theUVLED sources in the first UVLED array are driven at substantially thesame current.
 3. The method according to claim 1, wherein at least twoof the UVLED sources in the first UVLED array are driven at differentcurrents.
 4. The method according to claim 1, wherein: the outputx_(n)(t) of each UVLED source in the first UVLED array defines a pulsetrain with a duty cycle equal to A/B; each UVLED source in the firstUVLED array has substantially the same maximum output intensityx_(n)(t)_(max) and substantially the same minimum output intensityx_(n)(t)_(min); the first UVLED array has B UVLED sources; andx_(total)(t,v_(f))≈A(x_(n)(t)_(max)+x_(n)(t)_(min)).
 5. The methodaccording to claim 1, comprising the step of adjusting the phase of theoutput of at least one UVLED source in response to a change in the linespeed v_(f) of the glass fiber so that x_(total)(t,v_(f)) has asubstantially constant value for a given line speed.
 6. The methodaccording to claim 1, comprising the step of increasing the outputintensity of one or more of the UVLED sources in the first UVLED arrayin response to an increase in the line speed v_(f) of the glass fiber.7. The method according to claim 1, comprising the step of decreasingthe output intensity of one or more of the UVLED sources in the firstUVLED array in response to a decrease in the line speed v_(f) of theglass fiber.
 8. A method of curing a coating on a glass fiber,comprising: passing a glass fiber having an incompletely cured coatingat a line speed v_(f) through a cavity and along a curing axis that isdefined by the cavity; driving a plurality of UVLED sources that definea first UVLED array, each UVLED source in the first UVLED array beingdriven at a current that is greater than its maximum rated current,wherein each UVLED source in the first UVLED array has an oscillatingoutput x_(n)(t) of UV radiation having a maximum output intensityx_(n)(t)_(max) and a minimum output intensity x_(n)(t)_(min), themaximum output intensity x_(n)(t)_(max) of each UVLED source in thefirst UVLED array being greater than could be achieved if each of theUVLED sources was driven at its maximum rated current; and emitting UVradiation from the first UVLED array into the cavity to promote thecuring of the coating.
 9. The method according to claim 8, wherein theoutput of each UVLED source in the first UVLED array defines a pulsetrain.
 10. The method according to claim 8, wherein: the first UVLEDarray defines a normalized sum x_(total)(t,v_(f)):${{x_{total}\left( {t,v_{f}} \right)} = {{x_{1}(t)} + {\sum\limits_{n = 2}^{k}{x_{n}\left( {t + \frac{d_{n}}{v_{f}}} \right)}}}},$k=number of the UVLED sources in the first UVLED array, d_(n)=distancealong the curing axis from a first UVLED source to an n^(th) UVLEDsource; and at a given line speed, x_(total)(t,v_(f)) has asubstantially constant value.
 11. The method according to claim 10,wherein the first UVLED source and at least one other UVLED source inthe first UVLED array are separated along the curing axis.
 12. Themethod according to claim 11, wherein: the output x_(n)(t) of each UVLEDsource in the first UVLED array defines a pulse train with a duty cycleequal to A/B; each UVLED source in the first UVLED array hassubstantially the same maximum output intensity x_(n)(t)_(max) andsubstantially the same minimum output intensity x_(n)(t)_(min); thefirst UVLED array has B UVLED sources; andx_(total)(t,v_(f))≈A(x_(n)(t)_(max)+x_(n)(t)_(min)).
 13. The methodaccording to claim 11, comprising the step of adjusting the phase of theoutput of at least one UVLED source in the first UVLED array in responseto a change in the line speed v_(f) of the glass fiber so thatx_(total)(t,v_(f)) has a substantially constant value for a given linespeed.
 14. The method according to claim 8, comprising the step ofincreasing the output intensity of one or more of the UVLED sources inthe first UVLED array in response to an increase in the line speed v_(f)of the glass fiber.
 15. The method according to claim 8, comprising thestep of decreasing the output intensity of one or more of the UVLEDsources in the first UVLED array in response to a decrease in the linespeed v_(f) of the glass fiber.
 16. The method according to claim 8,comprising: driving a plurality of UVLED sources that define a secondUVLED array, each UVLED source in the second UVLED array being driven ata current that is greater than its maximum rated current, wherein eachUVLED source in the second UVLED array has an oscillating outputy_(n)(t) of UV radiation having a maximum output intensityy_(n)(t)_(max) and a minimum output intensity y_(n)(t)_(min), themaximum output intensity y_(n)(t)_(max) of each UVLED source in thesecond UVLED array being greater than could be achieved if each of theUVLED sources was driven at its maximum rated current, and wherein themaximum output intensity y_(n)(t)_(max) of at least one UVLED source inthe second UVLED array is different from the maximum output intensityx_(n)(t)_(max) of at least one UVLED source in the first UVLED array;and directing UV radiation from the second UVLED array to promote thecuring of the coating.
 17. The method according to claim 8, wherein themaximum output intensity x_(n)(t)_(max) of each UVLED source in thefirst UVLED array is substantially the same.
 18. The method according toclaim 8, wherein, for at least two of the UVLED sources in the firstUVLED array, the maximum output intensities x_(n)(t)_(max) aredifferent.
 19. An apparatus for curing a coated glass fiber, comprising:a cavity defining a curing axis; and a first UVLED array positionedwithin said cavity, said first UVLED array comprising a plurality ofUVLED sources; wherein each UVLED source in said first UVLED array isconfigured to have an oscillating output x_(n)(t) of UV radiation havinga maximum output intensity x_(n)(t)_(max) and a minimum output intensityx_(n)(t)_(min); wherein at least two of said UVLED sources in said firstUVLED array are configured to have oscillating outputs of UV radiationthat are out of phase with one another; wherein at least two of saidUVLED sources in said first UVLED array are separated along the curingaxis; and wherein said first UVLED array is configured to define anormalized sum x_(total)(t,v_(f)):${{x_{total}\left( {t,v_{f}} \right)} = {{x_{1}(t)} + {\sum\limits_{n = 2}^{k}{x_{n}\left( {t + \frac{d_{n}}{v_{f}}} \right)}}}},$k=number of said UVLED sources in said first UVLED array, d_(n)=distancealong the curing axis from a first UVLED source to an n^(th) UVLEDsource, v_(f)=line speed of a coated glass fiber as it passes throughsaid cavity and along the curing axis, x_(total)(t,v_(f)) having asubstantially constant value for a given line speed.
 20. The apparatusaccording to claim 19, comprising a controller electrically connected tosaid first UVLED array, wherein said controller is capable of adjustingthe output intensity and/or phase of the oscillating outputs of saidUVLED sources in said first UVLED array.
 21. The apparatus according toclaim 19, wherein each said UVLED source in said first UVLED array isconfigured to have substantially the same maximum output intensityx_(n)(t)_(max).
 22. The apparatus according to claim 19, wherein atleast two of said UVLED sources in said first UVLED array are configuredto have different maximum output intensities x_(n)(t)_(max).
 23. Theapparatus according to claim 19, wherein: the output x_(n)(t) of eachsaid UVLED source in said first UVLED array defines a pulse train with aduty cycle equal to A/B; each UVLED source in said first UVLED array isconfigured to have substantially the same maximum output intensityx_(n)(t)_(max) and substantially the same minimum output intensityx_(n)(t)_(min); said first UVLED array has B UVLED sources, whereby B=k;andx_(total)(t,v_(f))≈A(x_(n)(t)_(max)+x_(n)(t)_(min)).
 24. An apparatusfor curing a coated glass fiber, comprising: a cavity defining a curingaxis; and a first UVLED array positioned within said cavity, said firstUVLED array comprising a plurality of UVLED sources; wherein each UVLEDsource in said first UVLED array is configured to have an oscillatingoutput x_(n)(t) of UV radiation having a maximum output intensityx_(n)(t)_(max) and a minimum output intensity x_(n)(t)_(min), each UVLEDsource in said first UVLED array being configured to have a maximumoutput intensity x_(n)(t)_(max) that is greater than can be achieved bydriving each UVLED source at its maximum rated current; and wherein atleast two of said UVLED sources in said first UVLED array are configuredto have oscillating outputs of UV radiation that are out of phase withone another.
 25. The apparatus according to claim 24, comprising acontroller electrically connected to said first UVLED array, whereinsaid controller is capable of adjusting the output intensity and/orphase of the oscillating outputs of said UVLED sources in said firstUVLED array.
 26. The apparatus according to claim 25, wherein saidcontroller is configured to adjust the oscillating outputs of said UVLEDsources in said first UVLED array so that said first UVLED array definesa normalized sum x_(total)(t,v_(f)):${{x_{total}\left( {t,v_{f}} \right)} = {{x_{1}(t)} + {\sum\limits_{n = 2}^{k}{x_{n}\left( {t + \frac{d_{n}}{v_{f}}} \right)}}}},$k=number of said UVLED sources in said first UVLED array, d_(n)=distancealong the curing axis from a first UVLED source to an n^(th) UVLEDsource, v_(f)=line speed of a coated glass fiber as it passes throughsaid cavity and along the curing axis, x_(total)(t,v_(f)) having asubstantially constant value for a given line speed.
 27. The apparatusaccording to claim 24, wherein each said UVLED source in said firstUVLED array is configured to have substantially the same maximum outputintensity x_(n)(t)_(max).
 28. The apparatus according to claim 24,wherein at least two of said UVLED sources in said first UVLED array areconfigured to have different maximum output intensities x_(n)(t)_(max).29. The apparatus according to claim 24, wherein: at least two of saidUVLED sources in said first UVLED array are separated along the curingaxis; and said first UVLED array is configured to defines a normalizedsum x_(total)(t,v_(f)):${{x_{total}\left( {t,v_{f}} \right)} = {{x_{1}(t)} + {\sum\limits_{n = 2}^{k}{x_{n}\left( {t + \frac{d_{n}}{v_{f}}} \right)}}}},$k=number of said UVLED sources in said first UVLED array, d_(n)=distancealong the curing axis from a first UVLED source to an n^(th) UVLEDsource, v_(f)=line speed of a coated glass fiber as it passes throughsaid cavity and along the curing axis, x_(total)(t,v_(f)) having asubstantially constant value for a given line speed.
 30. The apparatusaccording to claim 29, wherein: the output x_(n)(t) of each said UVLEDsource in said first UVLED array defines a pulse train with a duty cycleequal to A/B; each UVLED source in said first UVLED array is configuredto have substantially the same maximum output intensity x_(n)(t)_(max)and substantially the same minimum output intensity x_(n)(t)_(min); saidfirst UVLED array has B UVLED sources, whereby B=k; andx_(total)(t,v_(f))≈A(x_(n)(t)_(max)+x_(n)(t)_(min)).
 31. The apparatusaccording to claim 24, comprising: a second UVLED array positionedwithin said cavity, said second UVLED array comprising a plurality ofUVLED sources; wherein each UVLED source in said second UVLED array isconfigured to have an oscillating output y_(n)(t) of UV radiation havinga maximum output intensity y_(n)(t)_(max) and a minimum output intensityy_(n)(t)_(min), each UVLED source in said second UVLED array beingconfigured to have a maximum output intensity y_(n)(t)_(max) that isgreater than can be achieved by driving each UVLED source at its maximumrated current; and wherein the maximum output intensity y_(n)(t)_(max)of at least one of said UVLED sources in said second UVLED array isdifferent from the maximum output intensity x_(n)(t)_(max) of at leastone of said UVLED sources in said first UVLED array.